NERVOUS SYSTEM OF THE FROG 15 



It will be seen on comparison with the value of C. for the series 

 of R. pipiens here used (C = 26.2) that these are much higher. 

 This implies an increase in the weight of the central nervous 

 system proportional to the differences in the values of C after 

 correction for the differences in body weights in the several 

 series. 



Why the particular series of pipiens used by me as a standard 

 falls below that for the two other series is a point the discussion 

 of which must be reserved for a future paper. 



In this connection it is desirable to refer to one modifying 

 condition affecting the value of C which has not heretofore been 

 mentioned, and the data on which are still unpublished. I find 

 that the value of C is not the same for specimens of R. pipiens 

 from different parts of our own country. For example those 

 coming from northern Minnesota give a value sensibly greater 

 than that found for the socalled "Chicago frogs" and the speci- 

 mens taken about Philadelphia give a value less than that found 

 for the " Chicago frogs," as a rule, but almost identical with that 

 of the series used as a standard in this paper. 



R. pipiens extends much farther south in this country of 

 course, being found both in Florida and Texas. What the rela- 

 tion of C may be in specimens from stations farther south than 

 Pennsylvania, has still to be determined, but the possibility of 

 variation in this character with latitude is a matter of much 

 interest. 



(F) THE RATIO OF THE WEIGHT OF THE BRAIN TO THAT OF THE 



SPINAL CORD 



Omitting the tabulation of the absolute values for the brain 

 and cord, as these can be readily found in the full tables, I give 

 below in table 12 a condensed statement of the ratios. 



It will be seen that in both 1904 and 1909, that relative weight of 

 brain (the value given under "ratio") is higher in R. esculenta 

 than in R. temporaria, although the difference is not so great in 

 the later as in the earlier records. Further, this ratio in R. 

 pipiens is always greater than in either of the European forms. 



Fiuallv it is to be noted that the ratios which I find for the 



